docs: def check_availability(self):
          """Check if resources from that dataset are available.
  
          Return a list of (boolean or 'unknown')
          """
          # Only check remote resources.
          remote_resources = [resource
                              for resource in self.resources
                              if resource.filetype == 'remote']
          if not remote_resources:
              return []
          return [resource.check_availability() for resource in remote_resources]